Every RS startup creates this NPE
[sync.1] wal.FSHLog: UNEXPECTED
2020-07-07 10:51:23,208 WARN [regionserver/xxxxx:16020] wal.FSHLog: Failed sync-before-close but no outstanding appends; closing WALjava.lang.NullPointerException
the reason is that the Disruptor frameworks starts the Syncrunner thread but the init of the writer happens after that. A simple null check in the Syncrunner will help here .
No major damage happens though since we handle Throwable Exception. It will good to solve this.